Hello Ken - Two points - (i) Current climate change is dominated by human forcing (greenhouse gas emissions, land use change) not the natural variations - and we have had a pretty good understanding of the direction of travel for decades - and indeed are observing the predictions unfold - and (ii) I'm not suggesting that we manage the climate system - that would be potentially dangerous and hubristic (though those enthusiastic for geo-engineering would disagree) - but that we manage human affairs - both to avoid the unmanageable and to manage the unavoidable.

Dear Ken - There's a powerful consilience of evidence - from the understanding of the basic physics of radiative transfer of heat through the atmosphere, through the observations from satellites, aircraft and in situ (energy accumulation in the ocean which receives some 94% of the planetary energy imbalance we have created, melting of the cryosphere, the geologically significant current 34cm/C of sea level rise after at least 2ky of stability, systematic warming of the surface and lower atmosphere, cooling and shrinkage of the upper atmosphere, increasing warm extremes and decreasing cold extremes, changes in atmospheric and ocean circulation, increased atmospheric water vapour which amplifies the CO2 and CH4 induced warming, responses of terrestrial and marine organisms and ecosystems, etc), to the insights from models. All this at a time when the planet would otherwise be gently cooling towards a new ice age and when the Sun has coincidently entered a slightly cooler state. The IPCC reports provide a detailed synthesis, and there are many other sources published as books or available on the Web, but if you want a quick summary (takes an hour or so to read) try '2071 - the World We'll Leave Our Grandchildren" (published by John Murray) which is the script of the play I wrote with Duncan Macmillan and performed at the Royal Court theatre in London and elsewhere. Apart from its direct impacts, human-induced climate change is recognised by the military and the security agencies as a 'threat multiplier' that worsens societal problems in an already troubled world. We are imperfectly adapted to the climate system we inherited (which was unusually stable) and certainly not adapted to the one we are provoking. A key way forward is to accelerate substantially the green technology revolution and aim to reach net zero carbon emissions as soon as possible - certainly by the 2050s. There's money to be made in the transition and there are major health and environmental co-benefits. Who wouldn't want to live in a world in which our energy needs are provided by clean, green technology and are inexhaustible? One last point, there's a lot of misinformation and indeed disinformation around generated by vested interests and by individuals who for one reason or another reject the reality. The Skeptical Science website debunks the raft of such arguments (https://www.skepticalscience.com) and the Climate Feedback site critiques individual media articles (some good, some terrible) (https://climatefeedback.org).

It's true that to reach net zero requires a gargantuan effort - but there are analyses that suggest that it is still doable without carbon capture (http://theenergymix.com/2018/04/19/1-5c-is-doable-without-controversial-carbon-capture-technique-new-study-concludes/). Personally I am skeptical about that, and even about scenarios such as Shell's recent "Sky" that indicate that staying below 2oC is still possible assuming BECCS and massive reforestation. But that doesn't mean that we shouldn't push as hard as possible in the direction of net zero. Sitting back and hoping that some form of natural cooling might help isn't a defensible approach. Try running a company risk management strategy on that basis! In any case, not only are natural fluctuations small compared with the human forcing, but they are as likely to increase the warming as reduce it (though the cooler Sun is helping a little). Best to fix the problem at the source than try and bandaid the symptoms!

It's true

Niranjan,

What's true?The statements of Chris or of Ken? What evidence do you have to backup your opinion?

Dear Ken - It doesn't take much searching on the web to find basic primers on climate change - ( for example: http://dels.nas.edu/resources/static-assets/exec-office-other/climate-change-full.pdf, https://climate.nasa.gov/scientific-consensus/, https://www.ucsusa.org/our-work/global-warming/science-and-impacts/global-warming-science#.Wt5F6C-ZNR4) and there's plenty of explanatory material (e.g; https://www.theguardian.com/environment/climate-consensus-97-per-cent/2014/may/06/top-ten-global-warming-skeptic-arguments-debunked, https://www.nrdc.org/stories/global-warming-101) - and as I pointed out in one of my earlier answers, the evidence that the world is warming and the climate system responding as a result of human actions is both empirical via a host of observations as well as being based on well-established laws of physics / chemistry / astronomy / biology. The conclusion that we need to stop adding CO2 (and CH4) to the atmosphere follows from assessments of the likely impacts - both direct and indirect - on human wellbeing and prosperity, and does not rely solely on computer models. Again, there are countless risk assessments downloadable from the web. Here are a couple of examples: http://www.csap.cam.ac.uk/media/uploads/files/1/climate-change--a-risk-assessment-v11.pdf, https://www.theccc.org.uk/tackling-climate-change/preparing-for-climate-change/uk-climate-change-risk-assessment-2017/. Its the case though that the estimates of the limit on cumulative emissions that would take us beyond 2oC of warming do depend on the models and so suffer some uncertainty - but uncertainty can cut either way! There's huge literature on the topic but here's an early example: http://geosci.uchicago.edu/~archer/warming_papers/allen.2009.trillionth_ton.pdf.

Both investigations and assistancecould go on simultaneously.

Dear Ken, I'd like to pick up a couple of your points. Firstly on the 70s predictions of cooling: a study of papers published at the time shows that the majority of published predictions were for warming (by a factor 6). The fact that the press picked up on the 'coming ice age' story is interesting but not an accurate reflection of what climate science was showing, even then. The Skeptical science summary of the situation follows. I should add that personally I'm not a fan of the "97% of climate scientists agree ..." argument, but I am convinced by the consilience of the array of evidence that human induced warming is real, and a threat that needs addressing.

https://www.skepticalscience.com/ice-age-predictions-in-1970s.htm

In the thirty years leading up to the 1970s, available temperature recordings suggested that there was a cooling trend. As a result some scientists suggested that the current inter-glacial period could rapidly draw to a close, which might result in the Earth plunging into a new ice ageover the next few centuries. This idea could have been reinforced by the knowledge that the smog that climatologists call ‘aerosols’ – emitted by human activities into the atmosphere– also caused cooling. In fact, as temperature recording has improved in coverage, it’s become apparent that the cooling trend was most pronounced in northern land areas and that global temperature trends were in fact relatively steady during the period prior to 1970.

At the same time as some scientists were suggesting we might be facing another ice age, a greater number published contradicting studies. Their papers showed that the growing amount of greenhouse gasses that humans were putting into the atmospherewould cause much greater warming – warming that would exert a much greater influence on global temperature than any possible natural or human-caused cooling effects.

By 1980 the predictions about ice ages had ceased, due to the overwhelming evidence contained in an increasing number of reports that warned of global warming. Unfortunately, the small number of predictions of an ice ageappeared to be much more interesting than those of global warming, so it was those sensational 'Ice Age' stories in the press that so many people tend to remember.

The fact is that around 1970 there were 6 times as many scientists predicting a warming rather than a cooling planet. Today, with 30+years more data to analyse, we've reached a clear scientific consensus: 97% of working climatescientists agree with the view that human beings are causing global warming.

See also: https://journals.ametsoc.org/doi/abs/10.1175/2008BAMS2370.1

THE MYTH OF THE 1970s GLOBAL COOLING SCIENTIFIC CONSENSUS

On your assertion that the planet hasn't warmed since the 97/98 El Nino (have I got that right?) and that the model predictions and unfolding reality haven't matched, have a look at (a) the plot attached from Ed Hawkins (Mapping global temperature changes every year from 1850 - 2017) (b) the plot of ocean heat content from NOAA (https://www.nodc.noaa.gov/OC5/3M_HEAT_CONTENT/), (c) a comparison of model predictions and temperature date from 2015 (see https://www.theguardian.com/environment/climate-consensus-97-per-cent/2015/aug/10/2015-global-temperatures-right-in-line-with-climate-model-predictions for a news article) and a plot of GISTEMP data up to 2017 - all of which contradict your position.

On your comment that "The history of past climates is generally ignored." a substantial body of literature exists estimating the climate sensitivity using data from past climates - see the IPCC (https://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch9s9-6-3.html), a Nature Editorial (https://www.nature.com/collections/lzprxrvxzf), and a random example (of many) https://www.geos.ed.ac.uk/people/homes/ghegerl/Hegerl_et_al_sensitivity.pdf

You say: "the web is filled with "climate change" discussions and assessments" as if the jury is still out on the conclusions and consequences. Yet Not a single national science academy disputes or denies the scientific consensus around human-caused climate change, and 'truth has spoken to power' and power has taken the message seriously - in the form of the Paris accord. Of course there are remaining uncertainties - not least in how humanity will respond. And of course the task is gargantuan in scale and scope - "The Greatest Collective Action in Human History". But basic risk management dictates that even if the threats were of low probability (which they are not) given their high impacts they demand responsible attention. Under the circumstances it seems to me we should be applying our collective intellects to shifting humanity in the direction of net zero carbon emissions (and greater resilience) as hard and as fast as we can - not throwing our hands in the air and saying it's all too difficult.

Hence the point of my original question!

Dear Ken, as I said above, the fact that the press picked up on the 'coming ice age' story in the 70s is interesting but it's not an accurate reflection of what climate science was showing. The current state of scientific understanding at any given time isn't determined by Time magazine or a popular book, but by the scientific process in which material that's 'in play' (usually through peer reviewed publication) is critically scrutinised with contributions that are refuted being rejected to leave a residual that represents our best approximation to 'truth' based on the consilience of the remaining evidence. Sometimes the consilience is very robust with only a tiny chance of it being overturned by subsequent work. That's seen to be the case with the evidence that humans are warming the planet and that the consequences represent a threat. You can dispute it if you wish - skepticism is the basis of the scientific method - but it behoves you to provide an alternative explanation of all the evidence - not some cherry picked subset, and certainly not based on popular misrepresentations of the science from 5 decades ago! Individuals who have tried this (some for decades) haven't managed to do so yet - nor at the same time to show how the observations and other evidence that support the consilience are fatally flawed - but by all means have a go!

On the hiatus - yes, time has shown that it was a fluctuation in a noisy data set. Cherry picking small subsections of data from a time series of a parameter which has a spectrum of temporal variability allows you to pretty much show any gradient you like, but the temperature plot I provided above (and included here again) shows that warming is alive and well ... as is the heat accumulation in the oceans, which showed no temporary slowdown. The latter is important since the oceans accumulate 94% of the planetary energy imbalance we have induced, whereas the atmosphere picks up 1-2% and is so an inherently noisier signal, especially given the natural exchanges that occur on various timescale between the various energy reservoirs in the Earth system (ocean, atmosphere, land, ice, biosphere). I've included some more temperature plots just to emphasise the point - including two plots from Berkeley Earth (http://berkeleyearth.org/global-temperatures-2017/) which you may recall started out a s a skeptical exercise funded in part by the Koch Foundation. I also added a Berkeley earth comparison of model data and observations (over land) and just for reference a plot of CO2 which shows the present situation in the context of recent ice ages.

Oops - missed these two ...

Oh, and if you want a Nature paper that explains what happened to the hiatus have a look at : https://www.nature.com/articles/nature22315.epdf?referrer_access_token=f9APa1nd1yDw2wkgPqOMsdRgN0jAjWel9jnR3ZoTv0NuFtYPLl1PUnqxUYbpB1uVru_rIjRyseUxK8YNRXQS41-Xf6ZZogTkPn3KRcKavtILhD4coONJlcGDCKvzDODIkuk843_-Ed8uysUYSjoO1mnSC9MKgJe-AEdiQrYEil_J7dXfrqXcEk3aUKEwwbhH12BmIcywDhqQFLGneIRyuDq-iGDMvQ9bs296RKsMvriVpLKKET19wX4Rxx8PJsQLOVCtFCLtm40GStmoCYmpiQ%3D%3D&tracking_referrer=www.latimes.com

A popular account can be found at: https://www.spectator.co.uk/2017/06/the-great-myth-of-the-global-warming-pause/

and another at: http://www.latimes.com/science/sciencenow/la-sci-sn-global-warming-hiatus-20170503-htmlstory.html

Hello Ken - Your (coloured) temperature plot is essentially the first half of the one I included twice previously - which shows the 1940-60 dip followed by the strong warming ever since. In the 60s and 70s the cooling effect of human generated stratospheric aerosols was not well understood, and so it's true that some scientists speculated about the planet (gently) entering a new ice age. Andre Berger told me that the modellers of the astronomical Milankovic effect also made an error and concluded that the Holocene interglacial would be shorter (10ky) than actually would have been the case (30ky) if we had not staved off the next ice age as a result of our GHG emissions! The point is that the science has moved on from that stage of evolving understanding - massively - and the situation is now rather clear. You seem to rely a great deal on the the state of play 50 years ago. I prefer to look at the contemporary evidence.

On the temperature data, I think you are implying that the observations of a given year have changed over time - implying that there is some sort of fiddling going on (is that what you are saying?). If so, this is another tired old chestnut; all data are adjusted for instrument calibrations and different sources of data have to be reconciled (for example ocean 'bucket' temperatures are biassed relative to those taken from engine cooling intakes which dominated after the 1960s). The modern adjustments made to early data sets on the basis of improved insights and analysis have actually reduced the amount of relative warming since pre-industrial times. For a review of the common contrarian myth on temperature adjustments have a look at: http://berkeleyearth.org/understanding-adjustments-temperature-data/

You say that "Some journals will not even entertain a manuscript involving skepticism." Can you provide an example please? I would be interested to see a case.

By the way, how do you account for the extraordinary changes that are taking place in the Arctic? And, for example, the geologically significant and accelerating rise in global mean sea level? We know that sea level has been stable for at least a couple of thousand years, and now it's rising at 33cm/C, which is a third of the average rate during the 120m rise between the last ice age and the Holocene. We know from direct experience that this is recent, or sea levels would be ~7m higher than in Roman times, and my daily commute over the London flood plain says that's not so!

So what do you think a world 3-4oC warmer than pre-industrial would look like?

Because if we were to adopt your strategy that's where we would end up eventually - even if the climate sensitivity were to turn out to be at the low end of the possible range (which is hedging a huge bet - no)?

Some of the impacts are likely to be literally unmanageable. To adopt a stance that assumes otherwise requires that you have done the hard work to show that the probabilities of such outcomes are sufficiently low to be safely ignored. Have you done that? I would love to see your workings. Do you insure your house? If so, you have concluded consciously or otherwise that the impact of its loss is sufficiently great that it's worth an investment of a hundred $ a year or so to hedge your bets against a roughly 1/1000 probability of a devastating fire. With climate change, we are dealing with the future wellbeing and prosperity of large sections of humanity (let alone the other passengers on our little space ship) - so a 1/1000 risk threshold would seem on the high side. Financial institutions and organisations responsible for preventing flood plain inundations routinely have to protect against the 1/200 to 1/1000 probability events. So let's see your calculations.

Otherwise it would be reckless not to seek to mitigate emissions.

And that's what I and others are proposing. We've seen that growth in economic prosperity and carbon emissions can be decoupled (since 1990 the UK GDP has grown 65% whilst our C emissions have dropped 40%) and the rate at which the costs of wind and solar PV are falling continue to surprise the pundits - and are at grid parity with fossil fuels or better in many parts of the world.

I would be interested to understand why you are so defensive of the status quo? I fully accept that the combination of fossil fuels, capitalism and unusual climate stability has allowed humanity to prosper in an extraordinary fashion.

But the party is over and we need to face the unwitting and unintended downsides that science has revealed.

It's a huge challenge, and progress will surely not be as great as the science tells us is necessary - but why not apply your intellect to striving for a better - low carbon - future - managing the unavoidable and avoiding the unmanageable.

Which once again brings me back to my original question!

Any one else out there who might want to pitch in on specifically on the Q?

I don't think the scientific community should shift effort from investigating the climate system to helping society manage climate change. They are not trained in management or politics which are the skills needed to manage the change.What they should be doing is warning the public of the possibility of catastrophic changes to the climate which may occur when the "inevitable surprise" happens. Committee on Abrupt Climate Change (2002) Abrupt Climate Change: Inevitable Surprises, Alley, R., Marotzke, J., Nordhaus, W. D., Overpeck, J. T., Peteet, D. M., and et al. (eds), Washington, D.C., The National Academies Press.

We do not know what caused the abrupt warmings at the start of the Bølling-Allerød inter-stadial and Holocene inter-glacial, although, IMHO, it was the loss of sea ice in the North Atlantic, replaced at the start of the Younger Dryas, which was the forcing factor.

If we do pass a tipping point where temperatures jump by 10C in as little as three years as happened at the entry into the Holocene, [Alley, R. B. (2000) The two-mile time machine, Princeton, New Jersey, USA, Princeton University Press], then holding the temperature rise to less than 2C will be shown to be the pipe dream it always was.

I think climate scientists should concentrate on their job which is to understand the climate and predict the effects of anthropogenic climate change. Too many climate scientists, like Dr Towe, are turning a blind eye to catastrophic climate change that will occur when the Arctic sea ice melts away. Even if it does not cause an abrupt change in climate itself, it will speed the melting of the Greenland ice sheet and a subsequent 7 m rise in sea level.